Back to EveryPatent.com
| United States Patent |
5,546,232
|
|
Hirakawa
|
August 13, 1996
|
Two-group zoom lens
Abstract
A two-group zoom lens is provided which has a first lens group of negative
power and a second lens group of positive power, located in this order
from an object to be photographed. The first and second lens groups are
moved relative to one another to provide various degrees of magnification.
The first lens group includes a first lens of negative power, a second
lens of negative power, and a third lens of positive power. The second
lens group includes a fourth lens of positive power, a fifth lens of
positive power, a sixth lens of negative power, and a seventh lens of
positive power. The fifth lens is cemented to the sixth lens. The fifth
and sixth lenses satisfy the following conditions: (a) 0.1<n.sub.N
-n.sub.P <0.4; (b) -1.3<r.sub.c /f.sub.2 <-0.5; and (c) 0.6<d.sub.1-2
/f.sub.w <1.2; wherein, n.sub.P represents a refractive index of the fifth
lens, n.sub.N represents a refractive index of the sixth lens, r.sub.c
represents a radius of curvature of the cementing surface of the fifth and
sixth lenses, f.sub.2 represents a focal length of the second lens group,
d.sub.1-2 represents a distance between the first and second lens groups,
and f.sub.w represents a focal length of the entire zoom lens at a wide
angle extremity.
| Inventors:
|
Hirakawa; Jun (Tokyo, JP)
|
| Assignee:
|
Asahi Kogaku Kogyo Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
258992 |
| Filed:
|
June 13, 1994 |
Foreign Application Priority Data
| Current U.S. Class: |
359/691 |
| Intern'l Class: |
G02B 015/14 |
| Field of Search: |
359/691,676,680,681,682,793
|
References Cited
U.S. Patent Documents
| 4074931 | Feb., 1978 | Okudaira | 350/184.
|
| 4653876 | Mar., 1987 | Yamagata | 350/463.
|
| 4792215 | Dec., 1988 | Sato | 350/426.
|
| 4812022 | Mar., 1989 | Sato | 350/426.
|
| 4934797 | Jun., 1990 | Hirakawa | 350/432.
|
| 5076677 | Dec., 1991 | Sato | 359/680.
|
| 5155629 | Oct., 1992 | Ito et al. | 359/676.
|
| 5233474 | Aug., 1993 | Hirakawa | 359/717.
|
| 5270863 | Dec., 1993 | Uzawa | 359/682.
|
| 5278699 | Jan., 1994 | Ito et al. | 359/692.
|
| Foreign Patent Documents |
| 59-142515 | Aug., 1984 | JP.
| |
| 1185607 | Jul., 1989 | JP.
| |
| 1239516 | Sep., 1989 | JP.
| |
| 2167515 | Jun., 1990 | JP.
| |
| 4114115 | Apr., 1992 | JP.
| |
| 4261511 | Sep., 1992 | JP.
| |
Primary Examiner: Epps; Georgia Y.
Assistant Examiner: Bey; Dawn-Marie
Attorney, Agent or Firm: Greenblum & Bernstein P.L.C.
Claims
I claim:
1. A zoom lens comprising a first lens group of negative power and a second
lens group of positive power, located in this order from an object to be
photographed, said first and second lens groups being moved relative to
one another to provide various degrees of magnification, wherein;
said second lens group comprises a first lens of positive power, a second
lens of positive power, a third lens of negative power, and a fourth lens
of positive power, said second lens being cemented to said third lens;
wherein, distances between the lenses of said second lens group are
maintained constant during a zooming operation of said zoom lens; and
wherein said second and third lenses of said second lens group satisfy the
following relationships:
0.1<n.sub.N -n.sub.P <0.4 (a)
-1.3<r.sub.c /f.sub.2 <-0.5 (b)
0.6<d.sub.1-2 /f.sub.w <1.2 (c)
wherein,
n.sub.P represents a refractive index of said second lens,
n.sub.N represents a refractive index of said third lens,
r.sub.c represents a radius of curvature of a cementing surface of said
second and third lenses,
f.sub.2 represents a focal length of said second lens group,
d.sub.1-2 represents a distance between a surface of a lens of said first
lens group furthest the object to be photographed and a surface of said
first lens of said second lens groups closest to the object, at a wide
angle extremity, and
f.sub.w represents a focal length of said zoom lens at the wide angle
extremity.
2. A zoom lens of claim 1, wherein said first lens group is comprised of a
first lens of negative power, a second lens of negative power, and a third
lens of positive power.
3. A zoom lens comprising a first lens group of negative power and a second
lens group of positive power, located in this order from an object to be
photographed, said first and second lens groups being moved relative to
one another to provide various degrees of magnification,
said first lens group comprising a first meniscus lens of negative power
having a convex surface on a side of said first meniscus lens nearer to
the object, a second meniscus lens of negative power having a convex
surface on a side of said second meniscus lens nearer to an object image
surface, and a third meniscus lens of positive power having a convex
surface on a side of said third meniscus lens nearer to the object;
wherein, distances between the lenses of said second lens group are
maintained constant during zooming operation of said zoom lens; and
wherein said zoom lens satisfies the following relationship:
< f.sub.1 /r.sub.2-2 <1.2
wherein, f.sub.1 represents a focal length of said first lens group, and
r.sub.2-2 represents a radius of curvature of a second lens surface of said
second meniscus lens.
4. A zoom lens according to claim 1, wherein said zoom lens consists of
said first lens group and said second lens group.
5. A zoom lens according to claim 3, wherein said zoom lens consists of
said first lens group and said second lens group.
6. A zoom lens consisting of:
a first lens group of negative power, and a second lens group of positive
power, located in this order from an object to be photographed, said first
and second lens groups being moved relative to one another to change
magnification;
said second lens group comprising a first lens of positive power, a second
lens of positive power, a third lens of negative power, and a fourth lens
of positive power, said second lens being cemented to said third lens; and
wherein said second and third lenses satisfy the relationships:
0. 1<n.sub.N -n.sub.P <0.4
-1.3<r.sub.c /f.sub.2 <-0.5
0.6<d.sub.1-2 /f.sub.w <1.2
wherein,
n.sub.P represents a refractive index of said second lens,
n.sub.N represents a refractive index of said third lens,
r.sub.c represents a radius of curvature of a cementing surface of said
second and third lenses,
f.sub.2 represents a focal length of said second lens group,
d.sub.1-2 represents a distance between a surface of a lens of said first
lens group and a surface of a lens of said second lens group closest to
the object, and
f.sub.w represents a focal length of said zoom lens at a wide angle
extremity.
7. The zoom lens according to claim 6, said first lens group comprising a
first lens of negative power, a second lens of negative power and a third
lens of positive power.
8. A zoom lens consisting of a first lens group of negative power and a
second lens group of positive power, located in this order from an object
to be photographed, said first and second lens groups being moved relative
to one another to change magnification, wherein;
said first lens group comprising a first meniscus lens of negative power
having a convex surface on a side of said first meniscus lens nearer to
the object, a second meniscus lens of negative power having a convex
surface on a side of said second meniscus lens nearer an object image
surface, and a third meniscus lens of positive power having a convex
surface on a side of said third meniscus lens nearer to the object; and
wherein said zoom lens satisfies a following relationship:
0<f.sub.1 /r.sub.2-2 1.2
wherein,
f.sub.1 represents a focal length of said first lens group, and
r.sub.2-2 represents a radius of curvature of a second lens surface of said
second meniscus lens.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens with two lens groups (referred
to as a two-group zoom lens) of standard focal length range having a
magnification of approximately two, used with, for example, a single lens
reflex camera.
2. Description of Related Art
A conventional two-group zoom lens of standard focal length range having a
magnification of approximately two usually includes a positive and
negative lens groups, as disclosed in, for example, Japanese Unexamined
Patent Publication Nos. SHO 59-142515, 1-185607, HEI 1-239516 or HEI
4-114115, etc.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a less expensive and
more compact two-group zoom lens than conventional two-group zoom lenses
hitherto known. To achieve the object mentioned above, according to an
aspect of the present invention, a two-group zoom lens is provided which
has a first lens group of negative power and a second lens group of
positive power, located in this order from an object to be photographed.
The first and second lens groups are moved relative to one another to
provide various degrees of magnification. The first lens group includes a
first lens of negative power, a second lens of negative power, and a third
lens of positive power. The second lens group includes a fourth lens of
positive power, a fifth lens of positive power, a sixth lens of negative
power, and a seventh lens of positive power. The fifth lens is cemented to
the sixth lens. The fifth and sixth lenses satisfy the following
conditions: (a) 0.1<n.sub.N -n.sub.p< 0.4; (b) -1.3<r.sub.c /f.sub.2
<-0.5; and (c) 0.6<d.sub.1-2 /f.sub.w <1.2; wherein, n.sub.p represents a
refractive index of the fifth lens, n.sub.N represents a refractive index
of the sixth lens, r.sub.c represents a radius of curvature of the
cementing surface of the fifth and sixth lenses, f.sub.2 represents a
focal length of the second lens group, d.sub.1-2 represents a distance
between the first and second lens groups, and f.sub.w represents a focal
length of the entire zoom lens at a wide angle extremity.
According to another aspect of the present invention, a two-group zoom lens
is provided which has a first lens group of negative power and a second
lens group of positive power, located in this order from an object to be
photographed. The first and second lens groups are moved relative to one
another to provide various degrees of magnification. The first lens group
includes a first meniscus lens of negative power having a convex surface
on a side of the first meniscus lens nearer the object, a second meniscus
lens of negative power having a convex surface on a side of the second
meniscus lens nearer an object image surface, and a third meniscus lens of
positive power having a convex surface on a side of the third meniscus
lens nearer the object. The zoom lens satisfies the following
relationship: (d) 0<f.sub.1 /r.sub.2-2 <1.2; wherein, f.sub.1 represents a
focal length of the first lens group, and r.sub.2-2 represents a radius of
curvature of the second lens surface of the second meniscus lens.
The present disclosure relates to subject matter contained in Japanese
patent application No. HEI 5-141961 (filed on Jun. 14, 1993) which is
expressly incorporated herein by reference in its entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described below in detail with reference to the
accompanying drawings, in which;
FIG. 1 is a schematic view of a lens arrangement of a two-group zoom lens
at a wide-angle extremity, according to a first embodiment of the present
invention;
FIG. 2 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 1, at a wide-angle extremity;
FIG. 3 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 1, at an intermediate focal length;
FIG. 4 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 1, at a telephoto extremity;
FIG. 5 is a schematic view of a lens arrangement of the two-group zoom lens
at a wide-angle extremity, according to a second embodiment of the present
invention;
FIG. 6 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 5, at a wide-angle extremity;
FIG. 7 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 5, at an intermediate focal length;
FIG. 8 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 5, at a telephoto extremity;
FIG. 9 is a schematic view of a lens arrangement of the two-group zoom lens
at a wide-angle extremity, according to a third embodiment of the present
invention;
FIG. 10 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 9, at a wide-angle extremity;
FIG. 11 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 9, at an intermediate focal length; and,
FIG. 12 shows various aberration diagrams of the two-group zoom lens, as
shown in FIG. 9, at a telephoto extremity.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A two-group zoom lens, according to the present invention, includes a first
lens group I having three lenses (i.e., first, second and third lenses
I-1, I-2 and I-3B), and a second lens group II having four lenses (i.e.,
fourth, fifth, sixth and seventh lenses II-1, II-2, II-3 and II-4), with
II-2 and II-3 being cemented to each other.
Lenses II-2 and II-3 satisfy the requirements represented by the formulas
(a) and (b) below.
0.1<n.sub.N -n.sub.p< 0.4 (a)
wherein "n.sub.p " designates the refractive index of lens II-2, and
"n.sub.N " the refractive index of the sixth lens II-3.
-1.3<r.sub.c /f.sub.2 <-0.5 (b)
wherein "r.sub.c " designates the radius of curvature of the cementing
surface of lenses II-2 and II-3 and "f.sub.2 " the focal length of the
second lens group II, respectively.
In the second lens group II, lenses II-2 and II-3 which constitute a
cemented lens assembly have positive power and negative power,
respectively. In the present invention, the powers of lenses 5 and 6 are
preferably intensified not only to make the lens assembly small, but also
to enhance an aberration correction function. Moreover, due to the
adhesion of lenses II-2 and II-3, the lens assembly is minimally
influenced by possible manufacturing errors, resulting in a stable and
high productivity of the lens assembly with a low manufacturing cost.
The formula (a) specifies a difference in the refractive index between
lenses II-2 and II-3. If lenses II-2 and II-3 are made of materials which
do not satisfy the requirement represented by the formula (a), i.e., if
the refractive index difference is smaller than the lower limit (i.e.,
n=0.1), spherical aberration cannot be effectively corrected at the
cemented surface of II-2 and II-3. This leads to an increase in the coma.
Conversely, if the refractive index difference is larger than the upper
limit (i.e., n=0.4), the refractive index n.sub.p of the positive lens
II-2 becomes relatively small, and Petzval's sum increases. This makes it
difficult to compensate the curvature of image (i.e., field curvature) and
the astigmatism. In theory, the Petzval's sum can be decreased by
increasing the refractive index n.sub.N of the negative lens II-3, but
generally speaking, a lens material having a high refractive index is
expensive. Accordingly, a solution to the problem in which the refractive
index n.sub.N of the negative lens II-3 is increased is not practical from
an economical view point.
Preferably, in the present invention, the lens II-1 is made of a lens
material having a refractive index that is relatively high in order to
correct the aberration. This also ensures that the lens II-2 can be made
of a relatively inexpensive lens material having a relatively small
refractive index.
The formula (b) specifies the radius of curvature of the cementing surface
(i.e., mating surface) of lenses II-2 and II-3 to effectively correct the
spherical aberration.
Since the cementing surface of the second lens group II is a diverging
surface for correcting spherical aberration using the refractive index
difference obtained by the formula (a), it is not desirable that the
curvature of the cementing surface is smaller than the lower limit (i.e.,
-1.3). Conversely, if the curvature of the cementing surface is larger
than the upper limit (i.e., -0.5), a high-order aberration may undesirably
result.
The zooming range is defined by formula (c) below.
0.6<d.sub.1-2 /f.sub.w <1.2 (c)
wherein "d.sub.1-2 " designates the distance between the surface of
terminal lens in the first lens group facing the image surface and a
surface of the first lens in the second lens group facing the object side
at the wide-angle extremity, and "f.sub.w " the focal length of the entire
lens system at the wide-angle extremity, respectively.
The wide-angle extremity is extended as the distance d.sub.1-2 between the
first and second lens groups I and II increases, but if the value of
d.sub.1-2 /f.sub.w is larger than the upper limit (i.e, 1.2), the quantity
of marginal ray tends to be undesirably reduced. Conversely, if the value
of d.sub.1-2 /f.sub.w is smaller than the lower limit (i.e, 0.6), a large
magnification cannot be obtained.
The following formula (d) defines shape of the lens I-2 of the first lens
group I.
0<f.sub.1 /r.sub.2-2 <1.2 (d)
wherein "f.sub.1 " designates the focal length of the first lens group I,
and "r.sub.2-2 " the radius of curvature of the second surface of lens
I-2, facing the image surface, respectively.
As is well known, if the power of the negative lens (i.e., front lens
group) is increased to make a wide-angle lens or a zoom lens having an
wide-angle compact at a wide-angle position, the distortion is increased.
To prevent this, it is known to provide an additional weak positive lens
on a lens nearest to an object to be photographed, for example, as
disclosed in Japanese Unexamined Patent Publication Nos. HEI 4-114115, HEI
2-167515 or HEI 4-261511, etc. According to one of the most significant
features of the present invention, the surface of the negative second lens
that is located nearer an image of the object is a convex surface, instead
of the provision of an additional positive lens. The convex lens surface
functions to correct the distortion, similar to the additional positive
lens. Consequently, in the present invention, a compact zoom lens which
does not have an additional positive lens can be provided in which little
or no distortion occurs.
If the degree of convexity of the lens surface of the second lens, as
nearer the image surface is below the lower limit (i.e, 0) in the formula
(d), distortion cannot be effectively corrected. Conversely, if the degree
of convexity of the lens surface of the second lens nearer the image
surface is above the upper limit (i.e., 1.2), the negative power of the
second lens will be too weak to realize a wide-angle lens as a whole. In
theory, it is possible to provide an enhanced concave surface on the
surface of the second lens, as nearer the object to be photographed, to
obtain a sufficient positive power of the second lens, but a coma will
tend to occur.
First Embodiment:
FIG. 1 shows a lens arrangement of a two-group zoom lens at a wide-angle
extremity, according to a first embodiment of the present invention.
As mentioned above, the first lens group I, located in front of a diaphragm
S with respect to the object, comprises 1st, 2nd and 3rd lenses I-1, I-2,
and I-3 whereas the second lens group II located behind the diaphragm S
with respect to the object is comprises 4th, 5th, 6th and 7th lenses II-1,
II-2, II-3, and I-4, respectively. The lenses of the first lens group I
are all meniscus lenses, and lenses II-2 and II-3 of the second lens group
II are cemented to each other.
Numerical data of the lens system shown in FIG. 1 is shown in Table 1
below. Diagrams of various aberrations thereof at the shortest focal
length, intermediate focal length, and longest focal length extremity are
shown in FIGS. 2, 3 and 4, respectively. In FIGS. 2 through 4, "SA"
designates the spherical aberration and "SC" the sine condition. The
"d-line", "g-line" and "C-line" represent the chromatic and transverse
chromatic aberration, represented by the spherical aberration, at the
respective wavelengths. The term "S" represents the sagittal ray, and the
term "M" represents the meridional ray. In Table 1, "r" designates the
radius of curvature of each lens surface, "d" the lens thickness or the
distance between the lenses, "N" the refractive index, and ".nu." the Abbe
number, respectively.
TABLE 1
______________________________________
F.sub.NO = 1:4.2.about.4.9.about.5.9
f = 36.03.about.50.00.about.68.00
.omega. = 32.1.degree..about.23.3.degree..about.17.4.degree.
F.sub.B = 41.41.about.50.42.about.62.04
f.sub.1 = -54.610
f.sub.2 = 35.238
f.sub.w = 36.03
______________________________________
Surface No. r d N .nu.
______________________________________
1 38.966 2.00 1.77250
49.6
2 17.670 7.08
3 -47.206 1.60 1.68250
44.7
4 -61.564 0.50
5 21.018 2.54 1.80518
25.4
6 24.929 28.52-13.60-3.41 (variable)
stop 1.21
7 33.325 3.17 1.75500
52.3
8 -66.840 0.10
9 14.913 4.59 1.50378
66.8
10 -44.114 3.68 1.83400
37.2
11 13.983 4.36
12 -40.374 2.31 1.58267
46.4
13 -21.741
______________________________________
Second Embodiment:
FIG. 5 shows a lens arrangement of a two-group zoom lens at a wide-angle
extremity, according to a second embodiment of the present invention.
Numerical data of the lens system shown in FIG. 5 is shown in Table 2
below. Diagrams of various aberrations thereof at the shortest focal
length, intermediate focal length, and longest focal length extremity are
shown in FIGS. 6, 7 and 8, respectively.
TABLE 2
______________________________________
F.sub.NO = 1:4.2.about.4.9.about.5.9
f = 36.03.about.50.00.about.68.00
.omega. = 32.2.degree..about.23.4.degree..about.17.4.degree.
F.sub.B = 42.34.about.51.32.about.62.89
f.sub.1 = -54.828
f.sub.2 = 35.259
f.sub.w = 36.03
______________________________________
Surface No. r d N .nu.
______________________________________
1 36.069 2.00 1.79500
45.3
2 17.554 6.46
3 -71.175 1.60 1.80400
46.6
4 -137.630 0.50
5 22.681 2.63 1.80518
25.4
6 29.260 28.63-13.65-3.41 (variable).sub.--
stop 1.21
7 42.968 1.21 1.71299
53.9
8 -101.850 0.10
9 19.444 8.42 1.69680
56.5
10 -22.971 1.50 1.83400
37.2
11 15.854 3.66
12 -51.274 2.35 1.64328
47.9
13 -23.543
______________________________________
Third Embodiment:
FIG. 9 shows a lens arrangement of a two-group zoom lens at a wide-angle
extremity, according to a third embodiment of the present invention.
Numerical data of the lens system shown in FIG. 9 is shown in Table 3
below. Diagrams of various aberrations thereof at the shortest focal
length, intermediate focal length, and longest focal length extremity are
shown in FIGS. 10, 11 and 12, respectively.
TABLE 3
______________________________________
F.sub.NO = 1:3.9.about.4.6.about.5.9
f = 35.96.about.50.00.about.75.00
.omega. = 32.1.degree..about.23.4.degree..about.15.9.degree.
F.sub.B = 42.60.about.52.50.about.70.13
f.sub.1 = -49.063
f.sub.2 = 34.598
f.sub.w = 35.96
______________________________________
Surface No. r d N .nu.
______________________________________
1 39.540 1.65 1.77250
49.6
2 16.866 6.51
3 -103.932 1.60 1.80610
40.9
4 -518.960 0.10
5 22.598 2.77 1.80518
25.4
6 31.345 27.99-14.73-3.42 (variable)
stop 1.20
7 47.904 3.21 1.69680
55.5
8 -47.904 0.10
9 15.447 4.81 1.51633
64.1
10 -43.109 5.61 1.83400
37.2
11 15.150 3.68
12 -67.864 2.44 1.58267
46.4
13 -25.449
______________________________________
The values of the formulas (a), (b), (c) and (d) corresponding to the
first, second and third embodiments, are shown in table 4 below.
TABLE 4
______________________________________
formulas
formulas formulas formulas
(a) (b) (c) (d)
______________________________________
example 1
0.33022 -1.252 0.825 0.890
example 2
0.13720 -0.651 0.828 0.400
example 3
0.31767 -1.246 0.817 0.095
______________________________________
As can be seen from Table 4 above, all three embodiments satisfy the
requirements defined by the formulas (a), (b), (c) and (d). Moreover,
according to the present invention, the aberrations are fully corrected
throughout the entire focal length range from the wide-angle extremity to
the telephoto extremity in a two-group zoom lens.
As may be understood from the above discussion, according to the present
invention, a simple, compact and inexpensive two-group zoom lens of
standard focal length range, having a magnification of around 2 includes
fewer lenses, i.e., seven lenses. In general, to realize a compact zoom
lens, it was necessary to increase the negative power of the negative lens
or lenses of the second lens group, resulting in a deterioration of the
quality of the zoom lens due to manufacturing error. However, in the
present invention, lenses II-2 and II-3 having large powers are cemented
to each other, the zoom lens is not influenced as significantly by
manufacturing error. Hence, the zoom lenses can be inexpensively and
stably mass-produced.
Furthermore, if the first lens group includes three individual lenses in a
compact zoom lens having two lens groups, the distortion on the wide-angle
side tends to be a large negative value. However, according to another
aspect of the present invention, the second lens is made of a negative
meniscus lens whose surface that is located nearer the image surface is
convex. Hence, it is possible to eliminate the distortion while keeping
the whole lens system compact.
Top